Currently, the worldwide annual production of methionine is about 500,000 tons. Methionine is the first limiting amino acid in livestock of poultry and feed and, due to this, mainly applied as feed supplement.
In contrast to other industrial amino acids, methionine is almost exclusively applied as a racemate of D- and L-methionine which is produced by chemical synthesis. Since animals can metabolise both stereo-isomers of methionine, direct feed of the chemically produced racemic mixture is possible (D'Mello and Lewis, Effect of Nutrition Deficiencies in Animals: Amino Acids, Rechgigl (Ed.), CRC Handbook Series in Nutrition and Food, 441-490, 1978).
However, there is still a great interest in replacing the existing chemical production by a biotechnological process producing exclusively L-methionine. This is due to the fact that at lower levels of supplementation L-methionine is a better source of sulfur amino acids than D-methionine (Katz and Baker (1975) Poult. Sci. 545: 1667-74). Moreover, the chemical process uses rather hazardous chemicals and produces substantial waste streams. All these disadvantages of chemical production could be avoided by an efficient biotechnological process.
Fermentative production of fine chemicals such as amino acids, aromatic compounds, vitamins and cofactors is today typically carried out in microorganisms such as Corynebacterium glutamicum, Escherichia coli, Saccharomyces cerevisiae, Schizzosaccharomycs pombe, Pichia pastoris, Aspergillus niger, Bacillus subtilis, Ashbya gossypii, Kluyveromyces lactis, Kluyveromyces marxianus or Gluconobacter oxydans. 
Amino acids such as glutamate are thus produced using fermentation methods. For these purposes, certain microorganisms such as Escherichia coli (E. coli) and Corynebacterium glutamicum (C. glutamicum) have proven to be particularly suitable. The production of amino acids by fermentation also has inter alia the advantage that only L-amino acids are produced and that environmentally problematic chemicals such as solvents as they are typically used in chemical synthesis are avoided.
Some attempts in the prior art to produce fine chemicals such as amino acids, lipids, vitamins or carbohydrates in microorganisms such as E. coli and C. glutamicum have tried to achieve this goal by e.g. increasing the expression of genes involved in the biosynthetic pathways of the respective fine chemicals.
Attempts to increase production of e.g. lysine by upregulating the expression of genes being involved in the biosynthetic pathway of lysine production are e.g. described in WO 02/10209, WO 2006008097, WO2005059093 or in Cremer et al. (Appl. Environ. Microbiol, (1991), 57 (6), 1746-1752).
However, there is a continuing interest in identifying further targets in metabolic pathways which can be used to beneficially influence the production of methionine in microorganisms such as C. glutamicum. 